The present invention generally relates to the field of vacuum pumps useful to evacuate an enclosed space. More particularly, the invention details a vacuum pump which incorporates a variable speed motor rotationally driving a compressor. The motor is electronically controlled to increase in speed in inverse proportion to the density of the air or gas being evacuated from the enclosed space. Thereby, the compressor and motor operate at maximum efficiency, reducing the evacuation time and energy requirements.
The most common types of vacuum pumps are designed for constant displacement and/or constant speed operation. These vacuum pumps are designed to have a peak efficiency at a selected inlet and outlet air or gas density. During the time interval required to evacuate an enclosed space, these vacuum pumps operate at the peak efficiency for only a brief time. During the majority of the evacuation interval, the constant displacement constant speed vacuum pumps are not operating efficiently, requiring longer evacuation intervals and higher amounts of power. Furthermore, the weight and bulk of these types of vacuum pumps is adversely affected.
Additionally, current vacuum pumps generally utilize oil or a liquid lubricant for reducing friction and wear within moving components. For some applications, these lubricants may be a source of contamination for the air being evacuated from the enclosure. When the air is being exhausted to a clean environment, contamination is not acceptable. Thus it would be desirable to eliminate the necessity for liquid lubricants where there is a potential for contamination.
It is therefore an object of the present invention to provide a vacuum pump which operates efficiently throughout the evacuation interval. A further object of the invention is to provide a vacuum pump which does not require liquid lubricants which may potentially contaminate the evacuated exhaust stream.